As IEEE Std. 802.11 wireless local area network (WLAN) capabilities grow in popularity and become the standard for a wide array of consumer electronic products, designers must deal with efficiency problems inherent in the present state of the art. As such, much attention must be paid to preamble detection techniques when building IEEE Std. 802.11 enabled architectures.
In commonly used preamble detection techniques, a correlator is often utilized to distinguish between a known signal and noise. The output of the correlator is typically compared to a predetermined threshold and a signal is declared present if the threshold is exceeded. However, if the signal is variable, then the threshold must be dynamically adjusted. This approach is typically difficult and often ineffective. When there is amplitude uncertainty in the received signal, a common approach is to hardlimit the signal before correlation to remove amplitude variations. The correlator is also frequently hardlimited to match the signal.
However in multipath environments, the signal is typically altered as it is reflected and absorbed in a variable fashion by fixed and moving barriers. This reduces the crosscorrelation between the actual signal received and the ideal transmitted signal and, as a result, the probability of missed detection increases significantly. Furthermore, in multipath environments, the false alarm rate also increases significantly. In addition, as transmission frequencies increase and identification periods decrease, existing technologies will have an increasingly difficult time recognizing and identifying signals in the allotted time.